Monday, November 27, 2006

Male Chimps Prefer Older Mates

Chimpanzees may be our closest biological relatives, but male chimps appear to differ from male humans in one striking way -- they clearly prefer older females, according to new research.

Martin Muller of Boston University and his colleagues analyzed detailed data collected about the behavior patterns of chimps living in the Kibale National Park in Uganda from 1996 to 2003.

In contrast to humans, the researchers found, male chimps find older females more desirable, approaching them more often to mate, fighting more with other males over them and mating with them far more frequently than with younger females. That is true even for higher-ranking male chimps, which have more choice of mates. The findings confirm the earlier results of other researchers.

"Multiple lines of evidence indicate that unlike humans, female chimpanzees become more sexually attractive with age," the researchers report in the Nov. 21 issue of the journal Current Biology. "This study demonstrates that male chimpanzees do not merely disdain young females, but actively prefer older mothers to younger mothers."

The researchers attributed the difference to a combination of factors. Humans tend to form long-term bonds, which favor a younger female mate to maximize the chances of mating again. Chimps, in contrast, are promiscuous. In addition, female chimps are fertile throughout their lives, enabling them to have offspring even late in life.

Regardless of the explanation, the findings clearly show that chimps and humans have evolved differently in this important way, the researchers said.

-- Rob Stein

Devices Record Tiny Sea Quakes

Scientists from Columbia University's Lamont-Doherty Earth Observatory have made the first close recordings of micro-earthquakes stemming from the creation of a new seafloor, but not exactly as planned.

Marine geophysicists Maya Tolstoy and Felix Waldhauser recently learned that eight of the 12 seismometers they had set along a section of the East Pacific Rise off Mexico's coast in 2003 became trapped in fresh lava flows along the ocean's bottom. Nonetheless, the seismometers, which were stuck more than 8,000 feet underwater, were able to record tiny earthquakes that could not be detected on land.

"It's amazing that we know so little about something so fundamental to the planet," said Tolstoy, whose paper on the recordings was published on the Science Express Web site. "Even if we don't get the rest of the instruments back, we'll have learned quite a bit."

The eruption took place in January, after at least two years of seismic activity, and the instruments that remain trapped in the Pacific may be able to help forecast future underwater earthquakes. "Our success emphasizes the importance of real-time monitoring on the seafloor, so the next time we'll be collecting many different types of data the moment an eruption starts," Tolstoy said.

Scientists have targeted the East Pacific Rise as part of the National Science Foundation's Ridge 2000 program because it is one of three areas where the seafloor is actively spreading. As part of the program, a group of geologists, chemists and biologists is documenting crustal formation in the ocean to understand how Earth's crust is formed.

"Discovering new lava so soon after a seafloor eruption is a unique opportunity," said Donna Blackman, who heads Ridge 2000. "It allows Ridge researchers a rare chance to see how geologic processes affect the deep-sea ecosystems that thrive near hydrothermal vents."

-- Juliet Eilperin

Humpback Brains Prove Unusual

Humpback whales are unusual among cetaceans for having in their brains neural cells of a type that is also found in humans. The structure of the neurons, researchers say, promotes the speedy transmission of information and may play a role in supporting the humpback's complex social life and sophisticated ability to communicate.

A study in the current edition of the Anatomical Record reports that the humpback brain contains "islands" of neural cells in the cerebral cortex that are generally not seen in the smaller-toothed whales and dolphins, but are found in primates and other large-brained whales. The function of these "spindle" neurons is not well understood, but they are thought to be involved in processing thoughts and information and are affected by Alzheimer's disease and other debilitating brain disorders.

The study's authors, from the department of neuroscience at Mount Sinai School of Medicine in New York, say that spindle neurons probably first appeared in the common ancestor of humans about 15 million years ago, and that they are found in great apes and humans but not in lesser apes and other primates. In whales and dolphins they evolved earlier, possibly as early as 30 million years ago. It is possible that they were present in the ancestors of all whales and dolphins but remained and developed only in those with the largest brains during their evolution.

"Humpback whales exhibit complex social patterns that include intricate communication skills, coalition-formation, cooperation, cultural transmission and tool usage," the authors write. "It is thus likely that some of these abilities are related to comparable [tissue] complexity in brain organization in cetaceans and in hominids."

-- Marc Kaufman

© 2006 The Washington Post Company